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Paediatrics RACP Exam Study > Genetics > Flashcards

Genetics Flashcards

1
Q

Risk of first cousins having child with genetic problems?

A

5%

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2
Q

What proportion of genetic material is shared between first cousins?

A

1/8

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3
Q

If a patient has a de novo PTPN11 mutation (Noonan syndrome) how likely is the parents’ second child to have Noonan?

A

1-2% - possible gonadal mosaicism containing AD mutation

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4
Q

What is the most common mutation for achondroplasia?

A

c.1138G>A (p.Gly380Arg) variant in the FGFR3 gene on 4p16.3 is the cause in about 98% of individuals

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5
Q

What is the screening test for achondroplasia and what do you see?

A
  • Skeletal survey
  • rhizomelic shortening (femur, humerus)
  • vertebral scalloping
  • horizontal acetabular roof with ‘mickey mouse ear’ iliac wings
  • metaphyseal flaring (trumpet bone)
  • trident hand
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6
Q

How often is achondroplasia a de novo mutation?

A

80% - AD mutation

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7
Q

What is the rate of autism in the sibling of an affected individual?

A

3%

Population risk 0.02-0.04%

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8
Q

What is the most heritable psychiatric disorder?

A

Bipolar - 65% concordance in monozygotic twins

First degree relative 15%

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9
Q

What does a transcription factor do?

A

Regulates binding of RNA polymerase

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10
Q

Which type of mutation is the most pathological?

A

Frame shifting (anything not in a multiple of 3 more likely to frame shift)

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11
Q

PHOX2B mutations are associated with…

A

Congenital central hypoventilation syndrome

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12
Q

How do you diagnose Prader-Willi?

A

Methylation analysis of the Prader-Willi critical region.

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13
Q

What are the key features of Stickler Syndrome?

A
  • autosomal dominant, gene mutation causing defect in collagens type II, IX or XI
  • midface hypoplasia, Pierre-Robin sequence
  • severe myopia, glaucoma, cataracts, retinal detachment
  • hearing loss
  • hypermobile joints - early arthritis
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14
Q

What can you NOT diagnose on regular karyotype?

A

Microdeletion

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15
Q

What gene is involved with Friedrich ataxia?

A

FXN1 (Frataxin) on 9q13 with a GAA repeat expansion in 96% - the size of the repeat on the smaller allele predicts severity

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16
Q

What are the features of Bardet-Biedl syndrome?

A
  • AR, variable genes
  • Short, fat, stupid (intellectual disability)
  • Retinitis pigmentosa -> vision deteriorates
  • Polydactyly
  • Hypogonadism
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17
Q

What syndromes are associated with retinitis pigmentosa?

A
  • Bardet-Biedl
  • METABOLIC: Kearns-Sayre (mitochondrial ‘red ragged fibre’), Refsum (peroxisomal, high phytanic acid), abetalipoproteinaemia (no VLDL, steatorrhoea)
  • Usher (progressively deaf and blind)
  • INFECTIVE: neurosyphilis, toxoplasmosis
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18
Q

What are the features of Cornelia de Lange syndrome?

A
  • Mouth like foetal alcohol, but monobrow and upturned nose
  • Severe ID and self harm
  • Limb abnormalities, IUGR and short
  • Cardiac issues
  • Gut malrotation
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19
Q

What type of collagen defect can cause both Stickler and Marshall Syndrome?

A

COL11A1 gene - type XI collagen, also Type II collagen for Stickler

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20
Q

What are the features of Smith-Lemli-Opitz syndrome?

A
  • Microcephalic, micrognathia, micropenis (ambiguous genitalia in males)
  • adrenal insufficiency
  • syndactyly of 2nd and 3rd toes
  • severe intellectual disability
  • give cholesterol + bile salts
21
Q

If you see unilateral facial microsomia (incomplete development of the ear, nose, soft palate, lip, and mandible on one side of the body) you should suspect…

A

Goldenhar or occulo-auricular-vertebral syndrome

22
Q

What is the gene implicated in Kabuki syndrome?

A

MLL2

23
Q

If you see fuzzy, sparse hair think…

A
  • Menkes

- Netherton if ‘bamboo hair’ and erythroderma

24
Q

What does DNA polymerase do in PCR?

A
  • Extends the primers once they are affixed to the single strand
25
Q

If you have a blood film with giant platelets and history of bleeding, then it may be…

A
  • GP1B defect - Bernard Soulier syndrome, defect in vWF receptor
  • Distinguish from vWD by the fact that normal plasma doesn’t help.
26
Q

What gene is Zellweger most associated with?

A
  • PEX1 on long arm 7q21-22
27
Q

What syndromes are associated with dural ectasia?

A
  • Marfans (major criteria, 60% have)
  • NF
  • Osteogenesis imperfecta
28
Q

What are the characteristic facies of Williams syndrome?

A

“Elfin” facies

  • Broad forehead
  • Blue eyes with stellate pattern iris
  • Short nose with a broad tip, full cheeks
  • Wide mouth with full lips and dental issues eg. missing teeth
29
Q

You see a baby with red, scaly skin, bamboo hair, and who is failing to thrive…

A
  • Netherton syndrome

- Also get lots of allergies

30
Q

What is the gene associated with ARPKD?

A
  • PKHD1
31
Q

If you see a baby with a hypothalamic harmatoma, imperforate anus and funny digits (polydactyly/syndactyly) which syndrome do you think of?

A

Pallister-Hall

Also have kidney issues and bifid epiglottis

32
Q

What does DNA helicase do?

A

Unwinds DNA

33
Q

Which genes are missing in Prader-Willi?

A
  • Paternal imprinting i.e. no Dad copy

- 15q11-13

34
Q

Which genes are missing in Angelman?

A
  • Maternal imprinting i.e. no Mum copy

- 15q11-13

35
Q

Which genes are affected in Beckwith-Wiederman syndrome?

A
  • 11p15.5
  • Complicated imprinting - loss of IMPRINTING CONTROL is the cause of most cases
  • Loss of methylation at IC2 which means paternal overexpression of KCNQ1OT1 (50%)
  • Paternal UPD 11 (20%)
  • Gain of methylation at IC1 (~5%)
  • Mutation of CDKN1C (<5%)
36
Q

There is a neonate with cleft, polydactyly, holoprosencephaly and possibly and omphalocele who has:

A
  • Patau aka Trisomy 13
37
Q

What genetic area is involved with Williams syndrome?

A

7q11.23, elastin gene

38
Q

What is a microarray for?

A
  • Microarray AKA molecular karyotype: micro-deletion and micro-duplication, copy number variants, homozygosity
  • Does NOT detect point mutations, very very small duplications and deletions of DNA segments within a single gene (Fragile X syndrome, for example) or balanced chromosomal rearrangements (balanced translocations, inversions)
39
Q

For a traditional karyotype, when do we pause cell cycle?

A

Metaphase/mitotic division - aiming to get maximally contracted DNA to make it easier to see the chromosomes

40
Q

What do you specifically find on traditional karyotype?

A
  • Karyotype: ring chromosome, extra chromosomes
41
Q

There is a baby with macrocephaly and fusion of the coronal suture…

A
  • FGFR3-related craniosynostosis/Muenke Sydnrome
42
Q

Which HLA type is associated with narcolepsy?

A
  • HLADQB1
43
Q

In which metabolic disorders do you see cherry-red retinal spots?

A

Usually LIPID STORAGE disorders

  • Tay-Sachs
  • Farber disease
  • GM1 and GM2 gangliosidoses
  • Metachromatic leukodystrophy
  • Niemann–Pick disease
  • Sandhoff disease
  • Sialidosis
44
Q

What is the Angelman phenotype?

A

“Happy Puppet”

  • “Hyper” i.e. hypertonic, hyper-smiling/laughing, hyper-electric (seizure)
  • “Retarded” profound mental and growth retardation
  • widely spaced teeth
45
Q

Which are your typical disorders that affect calcium?

A
  • Hypocalcaemia DiGeorge (22q11)

- Hypercalcaemia Williams (7q11)

46
Q

What are the facies of 22q11?

A
  • Small mouth
  • Wide prominent nasal bridge/root
  • Small eyes that look far apart due to medial canthi being farther apart
  • Round ears, deficient upper helices
47
Q

What syndromes give you increased risk of coeliac disease?

A
  • Type I diabetes mellitus 4.5% (0.97–16.4%)
  • First degree relatives of coeliac patients ≈10%
  • Selective IgA deficiency 8%
  • Autoimmune thyroiditis 3%
  • Down syndrome 5-12%
  • Turner syndrome 6%
  • William syndrome 10%
48
Q

What is the typical Williams facial phenotype?

A

Broad forehead, short nose and full cheeks, an appearance that has been described as “elfin”

Paediatrics RACP Exam Study (30 decks)

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